Epidemiology of non-AD dementias

Abstract

Dementia is a common neurodegenerative disorder that affects about 10% of the population over 65 years of age. A distinction can be made between primary degenerative dementias and dementia secondary to other diseases. This review focuses on the primary non-Alzheimer's disease (AD) dementias: vascular dementia (VaD), dementia with Lewy bodies (DLB) and frontotemporal dementia (FTD). VaD is after AD most frequent subtype of dementia with a prevalence of about 1%, ranging from 0 to 10% mainly depending on the age group investigated and the criteria used. Its incidence rate is between 1.5 and 4.1 per 1000 person-years, with no clear difference between men and women and with possibly a higher incidence in East Asia compared to Canada and Europe. Most of the VaD cases are sporadic although there are some rare familial forms of VaD as cerebral autosomal dominant arteriopathy with subcortical infarctions and leukoencephalopathy and familial cerebral amyloid angiopathy. Important risk factors for sporadic VaD are cerebrovascular pathology (brain infarction, white matter lesions and brain atrophy), midlife hypertension, and diabetes leading to increasing risk ratios. A protective effect is often found for education and moderate use of alcohol. The association between VaD and amyloid β, cholesterol, and statin use remains unclear yet. DLB and FTD are less frequent forms of dementia with prevalence rates of, respectively, 0.1–0.6 and 0.002–0.015%. FTD affects people in their middle age, accounting for up to 10–20% of the presenile dementia cases. About 14% of the FTD cases are caused by an autosomal dominant tau-mutation. However, since the prevalence of sporadic FTD is relatively low, population-based epidemiological studies are hard to perform and no non-genetic risk factors are known yet. DLB is a relative common form of dementia in old age accounting for 15–20% of cases in hospital autopsy case-series. The only known possible risk factor for DLB is the presence of an apolipoprotein E ε4 allele.